1. Field of the Invention
The present invention relates to a coating material application method for applying a coating material in predetermined patterns from a nozzle to the surface of a substrate, and also relates to an apparatus for use in such a method. The method and apparatus of the present invention are used to form light-shielding films on the surfaces of high-luminance discharge lamps for automotive headlamps, for example.
2. Description of the Related Art
A typical conventional method of this kind has been disclosed by Japanese Laid-open Patent Application No. 8-126860, for example. In this method, when a case constituting a hybrid integrated circuit is joined to a printed circuit board by adhesion, a nozzle is disposed vertically above an application position on the case used as a substrate with a predetermined gap maintained therebetween. While the discharge port disposed at the tip of the nozzle continuously discharges an adhesive mainly containing silicone resin or UV resin as a coating material, the discharge port is moved in a noncontact condition in parallel with the lengthwise direction of the application position so as to apply the adhesive continuously in such a manner as to draw a line.
In the case of the conventional line-drawing application method, it is necessary to consider the viscosity and thixotropy of a coating material. In particular, if a coating material is not provided with thixotropy, the coating material spreads over the surface of a substrate, that is, an application surface, immediately after the coating material is applied in a predetermined pattern, whereby the shape of the pattern may be distorted. In addition, it is necessary to maintain the gap between the tip of the nozzle and the substrate used as an application surface appropriately at all times. If the gap between the tip of the nozzle and the application surface is smaller than a predetermined value, the applied coating material is crushed by the tip of the nozzle, whereby it is impossible to obtain films having desired width and thickness values. On the other hand, if the gap between the tip of the nozzle and the application surface is larger than the predetermined value, air is apt to enter the space between the discharged coating material and the application surface, and so-called pin holes are generated in films, thereby exerting serious effects on the application position, such as displacement, and the accuracy of the application width and thickness. Furthermore, even if the gap between the tip of the nozzle and the application surface can be maintained constant, the gap may change because of undulation, distortion and nonuniform thickness generated on the substrate used as an application surface, or because of nozzle replacement conducted for maintenance, thereby making application unstable.
When the conventional line-drawing application method is used at a step of applying an adhesive in a production process wherein two or more members are joined by adhesion, the application width and thickness are not required to be controlled highly accurately on the order of several .mu.m. Therefore, no problem has occurred. However, when the method is used to form a light-shielding film on the surface of a high-luminance discharge lamp for an automotive headlamp for example, highly accurate application is necessary, and serious problems have been caused.